Anti-perovskite carbides Ca6CSe4 and Sr6CSe4 for photovoltaics with similar optoelectronic properties to MAPbI3

Abstract

Anti-perovskites with better stability than halide perovskites demonstrate great potential as stable photovoltaic materials. In recent years, a few anti-nitride and -oxide perovskites have been designed as solar cell absorbers, however, anti-carbide perovskites have yet to be investigated for photovoltaic applications. Herein, through first-principles calculations, environmentally friendly anti-perovskite carbides M₆CCh₄ (M = Ca, Sr, Ba; Ch = S, Se, Te) with good stability are anticipated, which arise from the stable Cs₄PbX₆-perovskite structure. Unlike the isolated [PbX₆] octahedra in Cs₄PbX₆, the covalent bonding feature of C–Ch bonds makes the [M₆C] octahedra connected in M₆CCh₄ advantageous for photo-induced carrier transport. They also show low carrier effective mass (0.2m₀), small exciton binding energy (30–80 meV), and strong dielectric screening, causing high carrier mobility up to 300 cm² V⁻¹ s⁻¹. Among the M₆CCh₄ anti-perovskites, Ca₆CSe₄ and Sr₆CSe₄ with similar optoelectronic properties to MAPbI₃ (MA = CH₃NH₃) are screened as the best single-junction solar-cell absorbers. Their suitable direct bandgap (1.50 eV) and dipole-allowed optical transitions between band edges result in strong visible-light absorption (2 × 10⁵ cm⁻¹). The large simulated power conversion efficiency of 31% is implemented in Ca₆CSe₄ and Sr₆CSe₄. The prediction of anti-carbide perovskites M₆CCh₄ provides a novel perspective on high-performance optoelectronic materials.